Department of Physics, Institute for Physical Science and Technology Biophysics Program, University of Maryland, College Park, 20742-0001, USA.
Phys Rev Lett. 2012 Aug 3;109(5):058101. doi: 10.1103/PhysRevLett.109.058101. Epub 2012 Jul 31.
Guanine-rich sequences in nucleic acids can fold into G quadruplexes, in which four guanines on a single strand combine to form G-tetrad planes stabilized by metallic ions. Sequence motifs which are predicted to form a G quadruplex are found throughout the genome and are believed to regulate a variety of biological processes. Detailed knowledge of the kinetics of G-quadruplex folding and unfolding would provide critical insight into these processes. To probe its structural stability, we used optical tweezers to disrupt single molecules of a single-stranded DNA G4 quadruplex. Dynamic force spectroscopy was employed, in which the distribution of rupture forces was measured for different loading rates and used to infer the nature of the transition state barrier for unfolding of the structure. The distance and height of the energy barriers were extracted for two observed conformations. The energy barrier was found to be close to the folded conformation, resulting in a high disruption force despite the relatively low energy barrier height.
寡核苷酸中的鸟嘌呤富集序列可以折叠成 G 四联体，其中单链上的四个鸟嘌呤结合形成由金属离子稳定的 G-四联体平面。预测形成 G 四联体的序列基序遍布整个基因组，并被认为调节多种生物过程。对 G-四联体折叠和展开的动力学的详细了解将为这些过程提供关键的见解。为了探究其结构稳定性，我们使用光学镊子破坏单链 DNA G4 四联体的单个分子。采用动态力谱法，测量不同加载速率下的断裂力分布，并用于推断结构展开的过渡态势垒的性质。提取了两种观察到的构象的距离和能量势垒的高度。发现能量势垒接近于折叠构象，尽管能量势垒高度相对较低，但仍导致较高的破坏力。
